1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly to a semiconductor device including a silicon fuse, a fuse opening formed in insulating films above the silicon fuse, and a guard ring surrounding the silicon fuse.
2. Description of the Related Art
A fuse formed by a silicon film pattern (referred to as a silicon fuse) is widely used for redundancy circuits, programming, and changing setting voltages by adjusting resistance values. An insulating film is formed on an IC (integrated circuit) chip having a fuse. The part of the insulating film above the silicon fuse is made thinner than other parts of the insulating film so that a fuse opening is formed for disconnecting the fuse.
The problem with such an IC chip with a fuse is that moisture may enter through the fuse opening, which may impair the reliability and degrade the properties over time. Conventionally, various measures have been taken in order to prevent such failures. A typical method is to provide a guard ring around the silicon fuse (see, for example, Japanese patent no. 2695548).
FIGS. 6 through 8 schematically illustrate a conventional semiconductor device having a silicon fuse and a guard ring. FIG. 6 is a plan view, FIG. 7 is a cross-sectional view cut along a line X-X′ in FIG. 6, and FIG. 8 is a cross-sectional view cut along a line Y-Y′ in FIG. 6. In FIG. 6, the layer structures above the silicon film pattern are not shown, except for the position of the fuse opening.
A base insulating film 103 is formed on a semiconductor substrate 101. On the base insulating film 103, a silicon fuse 105 made of a silicon film, two silicon wiring patterns 107, and a silicon guard ring 109 are formed.
The two silicon wiring patterns 107 are connected to the ends of the silicon fuse 105.
The silicon guard ring 109 is disposed in such a manner as to surround the silicon fuse 105. The silicon guard ring 109 has cutout parts 109A at positions intersecting the silicon wiring patterns 107, so that the silicon guard ring 109 is insulated from the silicon wiring patterns 107.
An interlayer insulating film 111 (interlayer silicon film between silicon layer and metal wiring layer) is formed on the base insulating film 103 in such a manner as to cover the silicon fuse 105, the silicon wiring patterns 107, and the silicon guard ring 109.
A contact hole is formed in the interlayer insulating film 111 and on the silicon guard ring 109, so as to be formed along the position of the silicon guard ring 109. A metal material is implanted into the contact hole so that a first via guard ring 113 is formed. The contact hole and the first via guard ring 113 are not formed above the silicon wiring patterns 107 or the cutout parts 109A, so that the first via guard ring 113 is insulated from the silicon wiring patterns 107. The interlayer insulating film 111 is positioned above the silicon wiring patterns 107 and the cutout parts 109A, because the contact hole and the first via guard ring 113 are not formed above the silicon wiring patterns 107 or the cutout parts 109A.
A first metal wiring guard ring 115 made of a metal material is formed on the interlayer insulating film 111 and the first via guard ring 113. The first metal wiring guard ring 115 is formed in a ring shape surrounding the silicon fuse 105, along the positions of the silicon guard ring 109 and the cutout parts 109A.
An interlayer insulating film 117 (inter-metal-wiring-layer insulating film) is formed on the interlayer insulating film 111 in such a manner as to cover the first metal wiring guard ring 115.
A via hole is formed in the interlayer insulating film 117 and along the first metal wiring guard ring 115. A metal material is implanted into the via hole so that a second via guard ring 119 is formed. The second via guard ring 119 is formed in a ring shape along the first metal wiring guard ring 115.
A second metal wiring guard ring 121 made of a metal material is formed on the interlayer insulating film 117 and the second via guard ring 119. The second metal wiring guard ring 121 is formed in a ring shape along the second via guard ring 119.
A final protection film 123 is formed on the interlayer insulating film 117, in such a manner as to cover the second metal wiring guard ring 121.
The part of the insulating films above the silicon fuse 105 is made thinner than other parts of the insulating films so that a fuse opening 125 is formed.
As shown in FIG. 7, the first via guard ring 113 is partially cut out, in order to prevent a short circuit between the first via guard ring 113 and the silicon wiring patterns 107. The interlayer insulating film 111 is positioned at the cutout parts of the first via guard ring 113. The interface between the interlayer insulating film 111 and the first metal wiring guard ring 115 becomes a moisture transfer path extending from the fuse opening 125 to an internal circuit (not shown) provided outside the first metal wiring guard ring 115. Accordingly, a factor having an adverse impact on the reliability of the IC enters the internal circuit.